Photonic integrated circuit (PIC) technology is expected to play an increasingly important role in optical communications, imaging, computing, and sensing with the promise for significant reduction in cost and weight of these systems. Future advancement of this technology may be significantly dependent on the ability to develop better scalability, testability, high performance, and cost effectiveness for this technology.
Optical switches on PICs contain many cells which need to be optically interconnected. Switch topology requires a large number of optical channel crossings (or bridges) including intra-chip (over waveguides or other photonic elements) and inter-chip (over gaps between chips). Optical switches on PICs use surface grating couplers for optical input and output ports. The optical input and output ports are generally coupled to optical fibers and may be used for coupling to other PICs.
Existing waveguide crossing or optical channel crossing including same level waveguide crossing, crystallographically oriented mirror systems, and surface grating couplers for inter-chip optical connection. FIG. 1 shows a diagram of a same level waveguide crossing 100. Although the same level waveguide crossing 100 provides optical channel crossing, it cannot be used over trenches nor over gaps between chips.
FIG. 2 shows a schematic diagram of a crystallographically oriented mirror system 200 for waveguide crossing. System 200 includes two waveguides 202, 204, separated by a gap 206. Each waveguide 202, 204 includes an angled minor 208,210 to reflect light from waveguide 202 to waveguide 204. However, system 200 is constrained to fixed wafer crystallographic axes. Furthermore, AR coatings are necessary on the vertical facets 209, 211. However, coating on vertical and angled facets is technologically complex.
FIGS. 3A and 3B are diagrams illustrating a system 300 for surface grating couplers for inter-chip optical connection. System 300 includes an input waveguide 302, an input surface grating coupler (SGC) 304, an output SGC 306, and an output waveguide 308. One problem with this type of inter-chip optical connection is the problem of aligning inverted grating images.